Pseudomonas aeruginosa utilises its type III secretion system to kill the free-living amoeba Acanthamoeba castellanii

Abstract number: 1732_192

Saeed A., Abd H., Wretlind B., Sandström G.

Objectives:Pseudomonas aeruginosa is a free-living, extracellular and a common environmental bacterium. It is an opportunistic and nosocomial pathogen causing serious health problems. To compete its predators such as macrophages and environmental phagocytes it utilises different survival strategies such as biofilm and formation of micro-colonies. It also develops resistance mechanisms and produces virulence factors such as lipopolysaccharide, alginate as well as extracellular, quorum sensing regulated enzymes and toxins and type III secretion system (TTSS). The aim of this study is to examine the interaction between P. aeruginosa PA103 and Acanthamoeba castellanii.

Methods: Bacteria and amoebae were co-culture and the interaction was examined between P. aeruginosa PA103 and A. castellanii by co-cultivation, viable count, eosin staining, electron microscopy, apoptosis assay and statistical analysis.

Results: The results showed that P. aeruginosa PA103 induced necrosis and apoptosis to kill A. castellanii by the effects of TTSS proteins ExoU, ExoS, ExoT, and ExoY. In comparison, growth of Acanthamoeba cultured alone and co-cultured with TTSS mutant strain was not affected.

Conclusions: The results confirm the nature of P. aeruginosa as a strict extracellular bacterium that needs TTSS to survive in the environment since this system is able to kill its eukaryotic predators such as Acanthamoebae.